Wood which is in contact with concrete, such as in wooden building construction and wood which is in contact with soil for example fence posts, utility poles, railroad cross-ties and wooden supports, can be structurally degraded by the action of termites, ants and other boring insects. Insecticides are available to protect wood from the action of such pests.
In wooden building construction, wood in contact with concrete may be structurally degraded by action of one or more wood pests including but not limited to termites, ants and other boring insects. Present methods of preventing or retarding the advance of insects includes fumigation wherein the entire structure may be sealed and an insecticide released therein. Disadvantages of this method include ecological and human health concerns as well as the limited time until the fumigant is sufficiently reduced in concentration to permit insect ingress.
Although insecticides are effective against the action of the boring insects, the insecticides must be repeatedly applied at intervals of from a few days to a few months or a year to remain effective. If insecticides are applied by themselves in sufficient quantity to be effective over a period of time, they pose ecological concerns, human health, and may present unpleasant odors, soil leaching and volatility of the insecticide. Furthermore, even the greatest amounts of insecticides applied by themselves dissipate within a relatively short time and need to be reapplied.
A further disadvantage of conventional application methods is that the concentration of bioactive ingredients resulting from a single application of insecticide starts out well above the minimum level necessary for effectiveness, but decreases rapidly and within a relatively short period of time drops below the minimal effective level necessary to maintain a barrier.
To this end, a number of techniques for the controlled release of chemicals such as insecticides have been developed in recent years. These methods employ polymer matrices and microcapsules to release insecticide.
Cardarelli U.S. Pat. No. 4,400,374 discloses the use of polymer matrices generally made of polyethylene, polypropylene, ethylene vinyl acetate, polyamide, polystyrene, polyvinyl acetate, or polyurethane to control the release of insecticides such as the insecticide commercially available under the tradename Dursban. The polymer matrices disclosed in U.S. Pat. No. 4,400,374, incorporate porosigen and a porosity reducing agent which upon contact with soil moisture or an aqueous environment dissolves the matrix.
Similarly, Cardarelli U.S. Pat. No. 4,405,360 relates to a polymer release matrix which can be composed of polyamide, polyurethane, polyethylene, polypropylene, polystyrenes and other polymers. The control release mechanism works in combination with a porosigen to release a herbicide in a moist environment.
A disadvantage of the Cardarelli methods is the necessity of sufficient moisture to dissolve the matrix. Periods of dryness, while extending the life of the matrix, would result in a decrease in the insecticide concentration thereby permitting access to the insects. In addition, the longevity of the matrix is variable and dependent upon moisture content.
In addition, Wysong U.S. Pat. No. 4,435,383 teaches the use of a controlled release mechanism for insecticides including carbamates, organothiophosphates, organophosphates, perchlorinated organics and synthetic pyrethroids. The release mechanism comprises a hydrophobic barrier monomer namely styrene and/or methyl styrene in combination with a monomer selected from one or more unsaturated mono- or di-carboxylic acids.
Another reference, Tocker U.S. Pat. No. 4,282,209 discusses a process for the preparation of insecticide-polymer particles. The insecticide, methomyl, is used to control insects which attack a tobacco, cotton or agricultural crops. Methomyl is dissolved with polymers such as polyamides, urethanes and epoxies to provide extended residual insecticidal activity.
A second Tocker patent, U.S. Pat. No. 4,235,872, discloses the use of slow-release insecticide microcapsules having a core of methomyl surrounded by a cover of allaromatic, uncrosslinked polyurea. In the arrangement disclosed in this patent, methomyl is used to protect vegetables, field crops and fruit crops.
A sixth reference, Young et al. U.S. Pat. No. 4,198,441, discloses the use of insecticides such as Dursban in a controlled release matrix comprising an organopolysiloxane, a hydrolyzable silane and a hydrolyzable organic titanium.
Additionally, Young et al. U.S. Pat. No. 4,160,335 discloses a mode of dispersing insect control substances by applying stripes to sheets of cellophane. The insect control substance which can include Dursban is placed in a polymer as well.
Another method is described in an Australian patent AU-B-82443/91. In this patent, there is described two sheets of plastic drawn from supply rolls. The upper face of the lower sheet and the lower face of the upper sheet are drawn past respective coating rollers which apply a coating of pesticide (e.g. permethrin) in a volatile solvent to the faces of the sheets. The coated faces of the sheets are brought together by passing them between compressive rollers. The coated and pressed sheets are laid under building foundations, or placed around trees or plants to prevent termite attack. Disadvantages of this product and method include (1) severance of a layer permits rapid escape of the coating, and (2) the coating is not integral to the sheets thereby permitting faster diffusion through the sheets and limiting the effective life.
Coated granules have a pesticide absorbed onto a matrix such as clay and then coated with cross-linked resins which helps slow the release rate. Clay loses or releases pesticide over a short period of at most a few weeks.
Although the prior art does disclose the use of an insecticide incorporated into a polymer matrix as controlled release agents, none of the references teach the creation and maintenance of a completely effective exclusion zone lasting several years or more. It is desirable to create a zone so as to prevent any contact between the wood structure and insects capable of damaging such structures. A reliable exclusion zone is necessary to protect wood structures for periods of time substantially greater than one year.
Therefore, in view of the above, it is an object of this invention to provide a zone of insecticide to protect wooden structures. Such zone consisting of a long term low volatility barrier and a high volatility short term barrier to protect soil.
It is a further object of this invention to maintain an exclusion zone for relatively great lengths of time of about 10 to 20 years.